Heat treat hardening is a well known and convenient method for increasing the hardness and durability of a metal surface. A basic heat treat hardening assembly includes a heating device, such as an acetylene torch, and a quenching fluid such as water. By passing the torch over the surface and immediately quenching the heated surface, a hardened skin is produced on the metal. This hardened surface is much more resistant to wear and damage than an untreated metal surface.
The standard heating devices produce localized heating, such as an acetylene torch. Thus, there is a need for relative motion between the heating device and the workpart to permit the device to travel across a surface to be hardened. Generally, either the workpart or the heating device move along a predetermined travel path to provide relative motion therebetween and permit heating of the workpart surface. The travel path required is, of course, dependent upon the shape of the workpart.
For a workpart having multiple surfaces to be hardened this can be a complicated, labor intensive task. For example, a metal foundry casting flask is a workpart of this type. The casting flasks are generally four-sided, box-like members with multiple surfaces to be hardened on each side. Typically, the flask would be placed flat on a support surface and multiple passes by the heat treat hardening device would be required to harden the multiple surfaces on each side. The heat treat hardening device would then be moved to harden surfaces on another side of the flask. After all four sides had been flame hardened, the flask would then be turned over to access the wear surfaces that were previously resting on the support surface and were thus inaccessible. The prior art does not show an apparatus or method to flame harden workparts of this type in one simplified process.
For example, U.S. Pat. No. 2,867,556 to Tegen discloses a flame hardening apparatus including gas nozzles which surround multiple surfaces on a metal rail. The nozzles emit a quantity of flammable gasses which, when ignited, provide a sufficient heating source to heat treat the surface of the rail. Since the apparatus is designed to flame harden long metal rails, the apparatus moves along a linear travel path above the rail. A leading quench and a following quench are disposed on opposite sides of the nozzles and provide a flow of quenching fluid onto the rail. This apparatus does not lend itself, however, to flame hardening workparts requiring a non-linear, multi-directional travel path of the flame hardening device.
This problem has been addressed with regard to circular workparts in U.S. Pat. No. 1,711,835 to Davis. The '835 reference discloses a flame hardening assembly including two torch members disposed on opposite sides of a drum shaped workpart. The workpart rotates with respect to the torch members to provide even, uninterrupted heating of the workpart. The workpart is partially supported in a tank of quenching fluid, and as a surface of the workpart is heated the rotation immediately carries the heated surface into the tank. Thus, the apparatus can flame harden a workpart that requires a non-linear travel path thereof relative to the torch members. However, this reference is not suitable for non-circular workparts or workparts requiring a complex travel path of the heating device with respect to the workpart. Specifically, the prior art does not teach a method or apparatus that would be capable of flame hardening a multi-sided workpart such as a casting flask.